'Shrek Forever After'Fourth time will be the charm for 'Shrek Forever After.' The final (we think) installment in the 'Shrek' saga will easily dominate the box office when it opens this weekend. But estimates of how much the green ogre will gross have been all over the map, and the uncertainty has reverberated from Hollywood all the way to Wall Street.

On paper, the fourth 'Shrek' looks like an easy winner. The first three were all monster hits, with the most recent, 2007's 'Shrek the Third,' opening with $121.6 million on this same weekend three years ago, setting an all-time record for an animated feature's three-day debut. The new chapter will enjoy a massive 4,359-screen opening, with a record 2,373 of them showing the film in 3-D and 194 showings on IMAX screens, also a record. The surcharges for those 3-D and IMAX screenings offer the film a huge bonus its predecessors lacked. And with fellow DreamWorks toon 'How to Train Your Dragon' finally fading, 'Shrek' will be the weekend's top family draw. 'Shrek Forever After'Fourth time will be the charm for 'Shrek Forever After.' The final (we think) installment in the 'Shrek' saga will easily dominate the box office when it opens this weekend. But estimates of how much the green ogre will gross have been all over the map, and the uncertainty has reverberated from Hollywood all the way to Wall Street.

On paper, the fourth 'Shrek' looks like an easy winner. The first three were all monster hits, with the most recent, 2007's 'Shrek the Third,' opening with $121.6 million on this same weekend three years ago, setting an all-time record for an animated feature's three-day debut. The new chapter will enjoy a massive 4,359-screen opening, with a record 2,373 of them showing the film in 3D and 194 showings on IMAX screens, also a record. The surcharges for those 3D and IMAX screenings offer the film a huge bonus its predecessors lacked. And with fellow DreamWorks toon 'How to Train Your Dragon' finally fading, 'Shrek' will be the weekend's top family draw.

You would think that would be enough for, say, a $130 million opening, and while there have been some predictions along those lines, distributor Paramount is only forecasting a modest $80 million. Why the $50 million gap? Because 'Shrek the Third' wasn't so hot, and it squandered a lot of the franchise's good will. The fourth movie hasn't been getting great reviews either. More uncertainty comes from the handing of the franchise over to a new director and new writers, as well as the fact that no animated franchise has lasted 10 years and four installments. Did the series peak six years ago with 'Shrek 2'? Has Shrek jumped the shark?

Paramount's lowball estimate led DreamWorks' stock price to fluctuate this week. Then again, there was a similar stock slide over 'Dragon's' modest opening, and that film went on to become one of the biggest hits of the spring. 'Shrek' should also rake in plenty of cash over the long haul, at least until 'Toy Story 3' opens in a month. Paramount's rival studios are guessing it'll open with $100 million. We're guessing it'll open closer to that figure than to $80 million or $130 million

Will Forte in 'MacGruber'The weekend's other wide release, 'MacGruber,' will be the top comedy choice for young adults. Based on Will Forte's recurring 'Saturday Night Live' adventure spoof, it's the first movie in a decade to be adapted from an 'SNL' sketch, probably because those movies have a poor track record. It's opening on 2,551 screens, which is a decent number, but its R rating will keep younger viewers out. (They'll all be catching 'SNL' vets Mike Myers and Eddie Murphy in 'Shrek,' anyway.) For those reasons, the movie will be lucky to earn $15 million and open in fourth place.

'Shrek' will end 'Iron Man 2's' two-week reign atop the box office chart. A 45 percent drop in business from last week would bring its take down to $30 million this weekend, still a sum most movies would kill for during their third week of business.

'Robin Hood' will also move down a notch, landing in third place. Middling word of mouth suggests a 55 percent drop to no more than $20 million.

'Letters to Juliet' will still be the date movie of choice and will finish at No. 5. A modest 35 percent dip would yield a $9 million weekend.

Top 5 predictions:

1. 'Shrek Forever After,' $94 million
2. 'Iron Man 2,' $27 million
3. 'Robin Hood,' $19 million
4. 'MacGruber,' $14 million
5. 'Letters to Juliet,' $9 million

• Follow Gary Susman on Twitter @garysusman.